The taskforce charged with prosecuting US banks behind the excesses of the housing boom and bust has brought its first case – to mixed reviews.

President Barack Obama appointed New York attorney general Eric Schneiderman to head the Residential Mortgage-Backed Securities Working Group in January in his state of the union address. "This new unit will hold accountable those who broke the law, speed assistance to homeowners and help turn the page on an era of recklessness that hurt so many Americans," Obama said.

According to the complaint, Bear Stearns and its lending unit, EMC Mortgage, defrauded investors who purchased mortgage securities packaged by the companies from 2005 through 2007.

The suit argues that wrongdoing was widespread at the firm, and that Bear Stearns made material misrepresentations about the quality of the loans in the securities, ignoring warning signs of trouble ahead as they sold them to investors. The same allegations have been made in several private lawsuits brought against JP Morgan.

John Coffee, a professor at Columbia law school, said it was a "significant move" but said cynics were questioning both the timing and the target. "It's about time there was action, and this is a much broader case than we have seen so far, much broader than the risk-averse SEC [the US's top financial watchdog] would be prepared to bring," he said. "But it's Bear Stearns, not JP Morgan," he said.

Coffee said Schneiderman had recently been eclipsed by Benjamin Lawsky, head of the recently formed New York department of financial services. Lawsky brought a high-profile case against Standard Chartered in August over allegations of money laundering.

The case is similar to a number of private actions that have already been brought. In a statement, JP Morgan has claimed the case was brought "without ever offering us an opportunity to rebut the claims and without developing a full record — instead relying on recycled claims already made by private plaintiffs."

Coffee said: "They wanted to bring this case quickly. A cynic might say they wanted to bring it before the election to show they are doing something."

Peter Henning, a professor of law at Wayne State University, said the case was important because it was the first broad action brought by Obama's team. "The case says this was a pattern of behavior, not some small specific wrongdoing," he said.

"But then it's an action against a defunct firm. You aren't going to see any significant reforms here," he said. Henning also said he did not expect any money to back to mortgage holders. The case is likely to lead to a settlement that will be paid out to other large institutions, not individuals.

"If they are leading with their strongest suit, my reaction is largely a shrug of the shoulders," Henning said.

Annemarie McAvoy of Fordham University, a former federal prosecutor, said this case was likely to be the "opening salvo" in a series of cases. "Clearly there were a lot of problems. It hasn't been as easy for regulators to bring cases as they would have liked."